"feeling good" seems a bit generic here. I doubt he means the same thing as inspiration. The competitive nature of chess and the fact that it is a "game", is usually enough to motivate someone to work harder after winning a few games (ie warcraft). Where as in writing and writing software there are more mental blocks and success and gratifications are generally slower, and also harder to get back on track if you start "feeling bad". So I think discipline is more important in activities that takes longer to feel gratified.